This application claims the priority of German Patent Document 199 30 910.5, filed Jul. 2, 1999, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to an imaging system for motor vehicles and a method for displaying images in motor vehicles.
It is well-known that the view in the rearward direction to observe the following traffic from a motor vehicle is rendered possible by means of interior and outside mirrors. This applies both to cars, as well as to trucks and busses. The use and simplicity of such rearview and side view mirrors is undisputed. However, they have several limitations and drawbacks, for example, with respect to safety and economical driving.
One drawback of the interior or rearview mirror is the limitation of the view in the direction of the rear due to the rear window or passengers, located in the motor vehicle. Furthermore, the view by means of the left outside mirror is not complete, but rather has a so-called xe2x80x9cdead anglexe2x80x9d, which is frequently the cause of traffic accidents when changing lanes.
Another grave drawback of the rearview and side view mirrors is that for viewing purposes it is necessary to rotate the view to the side by an angle of approximately 30 degrees to 45 degrees. When the driver looks into the mirror, his attention to the view ahead is extremely limited. The reason lies in the fact that the distinct vision decreases very rapidly with the angular distance from the visual axis; and at a viewing angle exceeding 30 degrees only a weak recognition of outlines and shapes without clear distance perception is possible. This is not at all adequate to react quickly to unexpected traffic obstructions or situations on the street.
In addition, when driving in the dark, the reflection from headlights of other motor vehicles is intense in the outside mirrors and the interior rearview mirror. Owing to the blinding effect, this feature is very disturbing and fatigues the driver on long trips. Frequently it is also the cause of accidents.
Since the outside mirrors project beyond the side limits of the motor vehicle body, they can constitute an obstruction or danger for other traffic participants and also be damaged, for example, when driving through very narrow streets or very close to other traffic participants. In addition, the outside mirrors can become rapidly dirty due to their unprotected attachment to the car, thus impairing the view.
Another major drawback of the outside mirrors is their effect on the C value, the result of which is an economic drawback. When driving fast on country roads and freeways, the air resistance of the side mirrors increases the fuel consumption of cars by approximately 5% to 10%. Another disturbing factor is the wind noise, generated during the trip by turbulence at the side mirrors.
A known approach to solving the aforementioned problems lies in the use of cameras, which can be embedded, for example, in the vehicle body. The viewing angle around the vehicle can be significantly increased, for example, with several cameras behind and on the side of the body. Then the image shot with the cameras is displayed on a monitor in the interior of the motor vehicle.
However, the above solution has the drawback that the displayed image is very close to the viewer. In contrast to looking into the conventional rearview or side mirror, looking at the monitor requires that the eyes continuously readapt, a feature that fatigues the driver of the motor vehicle. When the driver""s line of vision is directed alternatingly forward through the windshield or backward through the rearview mirror, the eyes must accommodate and converge. In addition, the image on the monitor does not appear vertical in relation to the visual axis, since for space reasons it can hardly be attached in such a manner in the motor vehicle.
Another significant drawback of such systems is the intrinsic brightness of the monitor over a wide solid angle. Thus, the interior of the motor vehicle is significantly brightened in the dark; and the driver""s view in the direction of the outside is rendered significantly difficult.
Therefore, the object of the present invention is to provide an imaging system for motor vehicles, which enables a display with high image quality and offers a higher degree of ergonomics and safety in traffic. Furthermore, a method for displaying images in motor vehicles shall be disclosed. Such a method enables the motor vehicle driver to view images with high quality during the trip without diverting his attention or tiring him due to continuous readaptation of the eyes.
The inventive imaging system for motor vehicles comprises a holographic screen, which scatters incident narrow band light of one or more wavelengths at a predetermined solid angle, a projector to project images on the holographic screen, and a holographic, transparent ray uniter, which allows broad band ambient light to pass in essence unimpeded and which guides the narrow band light, coming from the holographic screen, to the viewer to produce a virtual image at the viewing location.
The invention combines the advantages of conventional rearview mirrors, such as high image quality and no necessity of readaptation at rapidly changing distances, with the advantages of camera systems. On the one hand, a high degree of ergonomics and image quality are achieved; and, on the other hand, safety and economic efficiency while driving are increased.
A camera system can be coupled to the imaging system of the invention. Said camera is focused on the rear and/or the side and thus delivers images from the outside of the motor vehicle to enable a view to the rear and/or to the side. From the driver""s viewpoint the ray uniter is mounted advantageously in front of and/or directly on the windshield of the motor vehicle. Preferably the ray uniter is designed as a holographic mirror or as a ray deflector with lens function. The projector can comprise lasers with the primary colors red, green and blue.
Preferably the projector has an image modulator, for example in the form of ferroelectric liquid modulators or micro mirror devices.
The ray uniter can be mounted on a transparent plate, which is made, for example, of glass or plastic. In particular, the holographic ray uniter is arranged in such a manner together with the holographic screen that the virtual image appears for the viewer enlarged behind the windshield, preferably at a distance of at least 1.5 meters, especially preferred at a distance of at least 3 meters.
Furthermore, there can be a device for coupling the imaging to vehicle control functions or preset driving situations. The ray uniter and/or the holographic screen is/are designed and/or arranged preferably in such a manner that the light cone coming from the ray uniter is limited to the possible dwelling space of the viewer""s eyes. Preferably the holographic screen and the ray uniter are designed and/or arranged in such a manner that they exhibit an imaging function.
The inventive method for displaying images in motor vehicles includes projecting images on a holographic screen and guiding the light rays, coming from the holographic screen, into a viewer""s eyes, whereby virtual images are produced in a surface cutout of the front window and/or windshield by means of a hologram, whose purpose is ray deflection and which is connected in series to the holographic screen. Thus, the ergonomics of driving motor vehicles is increased; and images of the outside can be offered with high quality to the motor vehicle driver, whereby the aforementioned drawbacks of rearview or side mirrors and monitors are overcome.
With this method the images can be taken with a camera system in order to enable, in the windshield, the view in the rearward direction and/or to the side. Preferably images of the view toward the rear and/or from the perspective of the vehicle side mirrors are faded into the peripheral area of the windshield. Preferably the angular distance between the visual axis of the vehicle driver in the direction of travel and the virtual image is less than 30 degrees, especially preferred approximately 10 degrees. Furthermore, the rear and side images from the motor vehicle can be displayed as a function of the driving states or the vehicle control functions.